The Weight-Loss Method

Finally, one variation on the weight-loss method— Fuel hose testing modified GM 9061 fill and plug method —applies for fuel line aspects of fuel containment—here the sample can be from an actual hose or its liner. 

Calibration is the largest source of error in the measurements. N0a permeation rates were determined by the rate of weight loss. Neighing errors amount to + 2%. The uncertainty in the NO/Oa titration method used to check the weight loss method is about 5%. Additional calibration errors of + 2% are caused by temperature variations of the permeation devices. 

Weight Loss. Of all the methods the weight loss method is the most simple, requiring only the calculation of the difference in weight as a function of time. However, the method also has some serious disadvantages, the major one being that no qualitative information can be obtained about the active ingredient. 

Meniscus Regression. The meniscus regression method is comparable to the weight loss method in its simplicity and rapidity. The increase in the length of the void space between the open end of the hollow fiber and the meniscus of the column of liquid is measured periodically using a Wilder Varibeam optical comparator which has been described by Weatherston et. al. (3). Since this instrument can also be used to measure tFe internal diameter of the fiber, the volume and therefore the weight of material lost can be calculated as a function of time. 

The Zn corrosion products in the dew represent only the soluble corrosion products. Information on the insoluble corrosion products was obtained only in the C3H6/NOX experiment in which weight loss determinations were made. It was found that the total Zn corrosion determined by the weight loss method was larger than that found in the dew and rinse. The difference is equal to the amount of insoluble corrosion product formed. 

The second indirect method is by measurement of the weight of ethylene oxide delivered from the feed containers to the sterilizer. This method assumes no leakage, liquefaction, or polymerization of ethylene oxide in the gas tines connecting the gas source to the sterilizer. It is recommended that the two indirect methods be used in conjunction with each other. The weight loss method ensures that the increase in pressure is in fact due to gas from the ethylene oxide feed container and not from diluent gas or some other source whereas the pressure method provides an ongoing index of gas concentration during the exposure period. Gas makeups should be automated and specified to be drawn from the ethylene oxide feed tanks, not from the diluent gas. Gas makeup may be controlled by pressure switches or by pressure transducers connected to solenoid valves controlling gas flow. 

Advantage Rapid and easy interpretation of the results it shows a good correlation with the weight-loss method. 

The corrosion rate data published in the literature are generally values averaged over a period of time. They are based on measurements of the loss of material (the weight loss method), of the ferrous ions present in the solution (photocolorimetric method), and of the pH change in the solution and on volumetric methods (collection of evolved hydrogen). Electrochemical procedures have frequently been used. Thus, corrosion current has been determined at the intersection of the initial or steady-state cathodic and anodic Tafel lines, or any of these lines with E=Another way in which information has been acquired is through Stem-Geary linear polarization and impedance analysis. 

A convenient method for assessing the extent of surface oxidation is the measurement of volatile content. This standard method measures the weight loss of the evolved gases on heating up to 950°C in an inert atmosphere. The composition of these gases consists of three principal components hydrogen, carbon monoxide, and carbon dioxide. The volatile content of normal furnace blacks is under 1.5%, and the volatile content of oxidized special grades is 2.0 to 9.5%. 

The method can detect low corrosion rates that would take a long time to detect with weight-loss methods. 

D 2688 1983 Test method for corrosivity of water in the absence of heat transfer (weight loss methods)... 

Both carbonates decompose to their oxides with the evolution of carbon dioxide. The decomposition temperature for calcium carbonate is in the temperature range 650-850 °C, whilst strontium carbonate decomposes between 950 and 1150°C. Hence the amount of calcium and strontium present in a mixture may be calculated from the weight losses due to the evolution of carbon dioxide at the lower and higher temperature ranges respectively. This method could be extended to the analysis of a three-component mixture, as barium carbonate is reported to decompose at an even higher temperature ( 1300 °C) than strontium carbonate. 

There is usually more than one test method to determine a performance because each test has its own behavior and meaning. As an example there are different tests used to determine the abrasion resistance of materials. There is the popular Taber abrasion test. It determines the weight loss of a plastic or other material after it is subjected to abrasion for a prescribed number of the abrader disk rotations (usually 1000). The abrader consists of an idling abrasive speed controlled rotating wheel with the load applied to the wheel. The abrasive action on the circular specimen is subjected to a rotary motion. 

This term is normally abbreviated to ERH. The ERH is deduced by extrapolating the weight loss values over a range of water activities greater and lesser than that of the product. Where the two lines intersect lies the water activity of the product. This extremely tedious and time consuming method has largely been superseded by instruments that measure the water activity directly. The ERH still has practical importance since it indicates the conditions under which the product can be stored without deterioration. 

The possible preparation of InAs by crystallization from the melt depends also on the liquidus shape (especially in the In-rich region). A summary of previous liquidus measurements was reported by De Winter and Pollack (1986) who employed a source dissolution method based on the equilibration, at a fixed temperature, of a known quantity of high-purity indium with single crystals of InAs, the weight loss of which was determined. The experiments were carried out under a flux of hydrogen purified via permeation through palladium. 

Determinations of active hydrogen with methyllithium and with methylmagnesium iodide were undertaken by Uytterhoeven and Fripiat (366). Only after outgassing at 600° or higher, did the results of both methods agree with each other and with the weight loss on calcination. The reactions proceeded more slowly than with Aerosil silica (195). Apparently, diffusion into the pores is hindered, especially with the Grignard compound. 

The solvent removal can also be followed by gravimetric analysis of the weight loss. This method is used to determine the time necessary for complete solvent removal. Shown in Fig. 29 are such drying curves for 5 mm diameter cy-hndrical samples prepared with 16 wt % and 20 wt % cyclohexane. It is seen that most of the solvent is removed within the first day. However, the samples are held for an additional four days to achieve a porous structure with minimal amount of residual solvent. 

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